DeNovo Constructors was retained to install an innovative dewatering system in three former water treatment lagoons. The dewatering of the water treatment solids is the first step in the overall closure of the lagoons which includes the consolidation of solids into one lagoon, stabilization and capping. The solids in the lagoon exhibited thixotropic characteristics which precluded conventional dewatering approaches. In each of the lagoons, DeNovo installed a 5 foot diameter slotted corrugated pipe, to an average depth of 20 feet, which served as a cofferdam. The pipe was advanced into the sediment by placing a re-slurry pump in the interior of the pipe/cofferdam. After the sediment was removed from the interior of each cofferdam, a specially designed sump structure consisting of a 24 inch slotted pipe and 36 inch slotted riser was then lowered into each cofferdam. The interstice between the 36 inch riser and cofferdam was backfilled with filter stone. The 24 inch slotted pipe was wrapped with a non-woven filter fabric. A submersible dewatering pump was installed at the bottom of each sump structure including piping and associated electrical controls. The project was completed within schedule and budget.